Direct injection in Otto cycle engines offers significant performance benefits for both two-stroke and four-stroke engines, including improved fuel economy, reduced exhaust emissions, improved transient response, and increased power. However, adaption of direct injection to a given engine may be confronted by one or more problems.
For example, mounting space in a cylinder head may be limited, and so the injector location may have to be compromised, possibly to the detriment of combustion performance.
Another example involves ignition of the fuel cloud created by a direct injector. Particularly when the injector is used to create a stratified charge in the center of the cylinder, ignition by spark plug may require either extending fragile electrodes into the cylinder space, or else compromising the ignition point by using a more conventional spark plug to the side.
Leaner air-fuel mixtures do not reliably ignite with conventional electric spark mechanisms. Moreover, effective combustion of the fuel-air mixture is often problematic. If the ignitor is located adjacent a relatively cool combustion chamber wall, as with a conventional spark plug, the rate of heat loss to the wall may lead to flame quench, incomplete combustion, increased fuel consumption, and increased hydrocarbon emissions.
In order to better ignite leaner mixtures, a much hotter electrical energy source is required. Furthermore, in certain engines, such as two-stroke engines, the fuel charge needs to be ignited very quickly.
One means of providing hotter ignition is a new type of ignitor, called a miniaturized railgun or railplug. Such an ignitor can produce a high velocity jet that is driven by both electromagnetic and thermal forces. U.S. Pat. No. 5,076,223, describes a plasma jet ignitor, or railplug, which utilizes a plasma injector. The railplug of the '223 patent operates on the principle of electromagnetics, wherein the electromagnetic accelerating force causes plasma to propagate down the railplug bore to achieve supersonic speeds at the muzzle exit. However, even if a conventional spark plug were replaced by a railplug, a separate fuel injector would still be needed, and packaging and ignition issues would remain.
The present invention relates to a novel association of a railplug ignitor with a fuel injector. The railplug produces a high velocity jet of plasma between two long slender electrodes which is accelerated into the combustion chamber by a combination of thermal and electromagnetic forces along the same path as the fuel being ignited since the ignited fuel passes through the bore of the railplug. The ignition is timed in relation to the injection.
In accordance with one embodiment of the present invention, a railplug is adapted for fitting over the nozzle of a fuel injector. A connection to ground for one railplug electrode is achieved through the railplug shell to the engine cylinder head, and a connection of the other railplug electrode to the ignition electronics is achieved through an insulated source terminal.
For a full understanding of the nature and objects of the present invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawings and the appended claims.